1. Field of the Invention
The present invention relates to novel aqueous silicone emulsions crosslinkable by catalysis with a tin monochelate and, more especially, crosslinkable into a thin layer by tin monochelate catalyzed polycondensation reaction.
2. Description of the Prior Art
Emulsions of the above type, which comprise silicones (namely, organosilicon polymers) and whether used alone or in admixture with organic compounds or polymers, have long been known to this art.
They can be used to produce nonadhesive and/or water-repellent coatings, crosslinked into thin films, namely, having thicknesses ranging from a few .mu.m to approximately 200 .mu.m, on a variety of substrates (supports), in particular on cellulose-based materials.
U.S. Pat. Nos. 4,127,460 and 4,288,356, French Pat. Nos. FR-A-2,401,195 and FR-A-2,419,961 and European Pat. No. EP-A-169,098 describe emulsions of this type in which the basic silicone polymer, which is a diorganopolysiloxane .alpha.,.omega.-diol oil having a viscosity not exceeding 500,000 mPa.s, is dispersed in an aqueous medium.
In contrast, U.S. Pat. Nos. 4,008,346 and 4,066,594 and DE-A No. 2,449,085 illustrate emulsions wherein the diorganopolysiloxane .alpha.,.omega.-diol is already emulsion polymerized; the latter is, therefore, in the form of an emulsion. In this case, .alpha.,.omega.-diol polymers having viscosities ranging from oils (500 to 500,000 mPa.s at 25.degree. C.) to resins (above 500,000 mPa.s at 25.degree. C.) may be employed in the final emulsion.
Crosslinking of these emulsions is catalyzed by tin compounds, the most widely employed of which being dialkyltin dicarboxylates such as dioctyltin or dibutyltin dilaurate and dioctyltin or dibutyltin 2-ethylhexanoate.
These catalysts are undoubtedly effective and can easily be formulated into an emulsion. However, when being emulsified and during crosslinking they present the disadvantage of releasing two molecules of fatty acids per molecule of catalyst, and these tend to foul the coating apparatus.
Furthermore, these well-known catalysts, which impart a satisfactory stability (pot life) to baths comprised thereof, may exhibit an inadequate reactivity when the emulsion is crosslinked by heating with the elimination of water.